Carrier telegraph repeater



2 Simms-SHEET 1- /NVENTOR LC. ROBERTS L. C. ROBERTS CARRIER TELEGRAPH REPEATER Aug. 12, 1952 Original Filed Dec. 30, 1942 wma M Aug. l2, 1952 c. ROBERTS CARRIER TELEGRPH REPEATER 2 SHEETS-SHEET 2 Original Filed Dec. 50, 1942.

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vl/Wrox? By L. C'. ROBERTS ATT RNEV Pafenred Aug. 12, 1952 CARRIER TELEGRAPH REPEATER Leland C. Roberts, West Orange, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York @riginal application December 30, 1942, Serial No.

470,575, now Patent No. 2,495,773, dated January 31, 1950. Divided and this application January 26, 1950, Serial No. 140,670

12 Claims.

This invention relates to printing telegraph apparatus systems and particularly to a teletypewriter exchange system.

rlhis application is a division of copendingk application Serial No. 470,575, liled December 30, 1942, now Patent No. 2,495,773, issued Jan. 31, 1950.

An object of the invention is to interconnect subscribers stations equipped to transmit and receive alternating-current signals over toll lines arranged to carry alternating-current signals. k Another object of the invention is to provide a regenerative repeater for regenerating attenuated or otherwise deteriorated alternatingcurrent signals.

Another object of the invention is to transpose the marking and spacing signal conditions of alternating current, such as no-current and current, respectively, to the opposite conditions of current and 11o-current, respectively, and vice versa.

The invention features signal level compensation apparatus associated individually with intertoll trunks whereby a substantial saving in apparatus to be installed and maintained is accomplished as contrasted with the provision pf signal level compensation apparatus associated with each subscribers loop since the number of trunks in a system is usually a small fraction of the number of subscribers loops served thereby.

In accordance with the invention, and as more fully described in the copending application, the subscribers stations are individually provided with a source of alternatingr current which generates alternating current at the signaling frequency. The application of trains of alternating current waves to the subscribers line is controlled by transmitting contacts, and transmitted alternating current as well as received alternating current is amplified by a local amplifier and is rectified for the purpose of operating a printing telegraph receiving recorder which records received messages, and in the case of locally generated signals, produces a home record of those signals. rThe subscribers station operates upon a basis of alternating current oil for marking signals and on for spacing signals, this arrangement providing for alternating current off at the subscribers station while signals are being received, so that the receiving amplifier is responsive to received trains of alternating-current waves without interference from locally generated alternating current, whereas it would not respend to received trains of alternating-current waves separated by 11o-current intervalsif the subscribers transmitter, in the idle condition,

2 should be applying steady alternating current to the receiving amplifier.

At the central oice station, cord circuits arranged to carry alternating-current signals between two subscribers line circuits or between a subscribers line circuit and a trunk circuit are individually associable by means of keys with an operators set which is similar to a subscribers transmitting and receiving set, in that it gencrates alternating current for signaling, amplifies and rectiiies received signals, and also amplies and rectilies locally generated signals for the operators home record.

Connections between subscribers served by different central oiiice stations are established over intertoll trunk circuits extending between the two central oice stations. At each end the receivingl sides of the trunk circuit are provided with receiving ampliers which have automatic gain control features. Since the gain of suchY ainpliiiers is at maximum when no signal is being receivedandsuch amplifiers will then be most sensitive to noise disturbances and also to the beginnings of incoming signals, itis preferable to have the lines interconnecting the central office stations energized by alternating current for the idle or marking condition in order to hold the gain of the receiving ampliers to normal level. Accordingly, at each end of the trunk in the transmitting side there is a signal conversion circuit for converting current-on spacing signals received from a cord circuit to current-orf spacing signals and, conversely, for converting currentoff marking signals received from a cord circuit to current-on marking signals.

When alternating-current trains of waves are transmitted over long toll lines the` signals may become impaired such as by tapering off of the amplitude of the beginnings or ends of the trains of waves, so that the duration of the portions of the trains of waves at effective amplitude may be materially reduced. For the correction of this conditionrthe invention includes a regenerative repeater for alternating-current signals which produces trains of alternating current at full amplitude for each received train of alternating current and which has timing means for allotting a full impulse interval to each produced train of alternating current independently of the duration of the portion of the received train which is of effective amplitude.

For a complete understanding of the invention', reference may be had to the following detailed description to `be interpreted in the light of th accompanying drawings wherein:

Fig. l is a diagrammatic View showing subscribers stations equipped to transmit and receive alternating-current signals, its line termination at a central oiice station, a cord circuit and operators set at the central oni-ce, an intertoll trunk circuiti extending to a remoteswitching oice station, and a cord circuit for extending a connection from the intertoll trunk at the remote. central oice;

Fig. 2 is a diagrammatic vievvfsh'otiirig` a rei-- generative repeater for regenerating alternatingcurrentsignals; and H y Y Fig. 3 is a diagrammaticView'showing how- Figs. 1 and 2 and a reverse or mirror image of Fig. 1, indicated in dotted outline; may bef-coni-A bined to show a complete'systerrr-for"intercorr-` necting two subscriber stations by trunks tandem through a regenerative repeater.'

Referring to the drawings and particularl'yito' Fig. l, the reference numeral ||l| designates a subscriber station whichis represented very generally in schematic form and-which! may be` of the typeshown in Fig. l of' thacoperdingl-applica-tion.V` Line conductors |013` and |84 that serveA the subscriber station terminate at that station inthe right-hand winding oftransformer |05 which is connectedkpa-rallelly to one winding of'Y each of'- the transformers i09"and |34'. B y Virtua ofI the presence oftransformers |55', [G9 andi|34 itwill be apparent thatsignal transmission to and from each subscriber 4station is on arr alternating-current basis. The transfarmers |59 and |34 connect receivingfa'nd transmitting equipment respectively toV the transfrmer-' iilnivT-he receiving equipment, designated-by' rererencenumerall |02"` includes'l ampli` f-ygir'ig` andl r'ectifying equipment;r as disclosed in Fig. 1=of the cope'nding application, for converting si'grialsto'A` direct current to operate a teletypewriter printer, and the transmittingapparatus', designated b y reference numeral |55 includesa source of alternating currentY for signal transe rrission,l as also shown in' Fig. llof the coperidapplication. Because of the fact that the receiving equipment |`B L" is coupled' to' transmitting eduip'ment ||i5l through transformers lii'and |3'4 the. receiving equipment is` arranged to' respend to' signals generatedby the'v transmitting equipment and impressed' through transformers |34 and V05" on the line conductors |53 arid-|4014', the response' of the receiving eduipmerltiV |'IJ`2"to` the outgoing signals providing a' home record ofy transmitted message material'.

Line conductors |63 and |04 extend to a` ceritral cnicev stationY Where they terminate in' the springs of line jackA |52. Jack |52v is" adapted to receive the answering plug2'l of'a -c'c'rd' circui-t 20|)-v which indicated only schematically in` Fig. 1 and complete details of which are containedV in Fig. 2` of the cc'p'ending application'. Associated'with the cord circuit 22E) is an' operat'e'rs'setI 33D, shown schematically in Figa l but shown in complete detail in Fig. 3 of th'eA copen'd'i'ng. application, by means ofA which an, oper'- ator, havingy answered a call from subscriber station |01 by the insertion of plug 29| jack |52',- communicates withthe subscriber for the purpose ofA ascertaining the destination` of the call initiated by the subscriber. The operator-s setv is equipped' to transmit and receive alternating-current signals'. TheY cord circuit 255 'is provided with signaling and supervisory apparatus asvis'f fully disclosed in the copending application'.n

As' is fully disclosed-in the copending application, signal transmission b'e'trree'n the subscriber station and the central oice over the subscribers line and through the cord circuit is on the basis of current for spacing signals and no current for marking signals. A reasonfor this is that the transmission ofy alternating current from the subscribers transmitter during idle marking condition thereof would mask spacing signals of no current transmitted from the central oice, if transmissicnl should be on the opposite basis of current for marking and no current for spacing.

Plug-124|" is'v the calling plug of cord circuit 25`0'and-i's' adapted to be in circuit in a jack associated with a telegraph circuit over which a call. initiate'oli` by" the subscriber station is to be extended. For' example, the plug 25| may be inserted` ii1`- jackl 45|. The springs of jack 40| are' connected` to conductors 452 and 455 that are'vbridged by inductance 453 and are also connected to the left-hand terminals of condensers 454 and-408, respectively.

The right-hand terminals of' the condenser-s 404 and: 458" are` connected'y by' conductors' 455 andY 4|5, resectively, to a hybrid coil `5|5 andthe spacing impulse trains oi alternating current flow through the condensers" 454 and 'M18 to this coil. The'conden'sers'44 and 458 block oi from the hybrid coil direct current which iicws in conductors' 452: and 455 for energizing a supervisory' relay, as described` in the` copending` application, and the iriductance` |53 provides a direct-current path i'or this current in addition to' serving as a' filter in` combination with' the co'nden'ser'sv A404` and'4i8. For reasons which will be described hereinafter', it is desirable' that` in the trunk circuit, marking signals` shall be represented by a flow-of' alternating' current and' spacing sign'al's'sliailA beL represented by ano1-current condition. Since' thisl is the opposite of the condition' in the` local subscribersl line andJ in the cordI circuit 205, it is necessary to provide a signal transposing circuit associated with the intertoll trunkcircuit.l This transposing circuit will now be described.

The spacing signals comprising trains ofl alternating'current' induce alternating currents at the same frequencies in windings 5| '|v and' 5|8 of the hybrid coil. These coils' are in series, and a condenser 5|9 shunted by a resistor 52| has one terminal connected to' the' point of interconnection of the-.two windings 5H and 5|8. The other e'nds-of the' windings 5|'| and 5|8 are connected throughY half-wave rectiiers 522 and 523 tothe other` terminal of condenser 5|9. This circuit serves as a full-wave rectier for' rectifying the spacing trains of alternating current received over conductorsr 452 and 40S and for charging condenser 5 9 with such rectified current. There is also connected across condenser 5|5 and resistancev 52| a circuit comprising a source of alternating current 526, which generates current at the signaling frequency, condenser 521, resistor 528, primary winding of transformer 529 and rectiiier 53|. When the full-wave rectifier circuit, including'rectifiers 522 and 523, is charging condenser 5|9, the condenser blocks the ow of current from alternating-current source 525 through the primary of transformer 529 so that no current flows in that winding of the transformer. When' current ceases in conductors 452 and 40S, which is the marking condition, condenser' 5|9 discharges and permits current to ow through the primary winding of transformer 529 and rectier 53| so that a marking signal of alternatingcurrent now is induced in the secondary of trans'- former 529. Thus as a result ofv any spacing signal comprising alternating current, no current is generated in the secondary winding of transformer 529. This winding of the transformer is connected through band-pass filter 532 to toll line conductors 533 and 534 which extend to the remote central oiiice station where they enter the receiving circuit of an intertoll trunk circuit identical with that shown in Fig. 1. In the signal transposing circuit, a battery 536 has one terminal connected through resistor 531, primary winding of transformer 529 to one terminal of rectiner 53| and the other terminal of the battery is connected through resistor 52| to the other terminal of rectifier 53|. This battery normally biases the rectier 53| so that it operates on the linear portion of its characteristic.

Since only one end of the intertoll trunk circuit has been shown in detail in Fig. 1, it is necessary to consider the effect of received call and other signals as if received from the remote station shown at the right of Fig. 1. Signals are received over a separate pair of receiving conductors designated by the reference numerals 54| and 542 and signals received over these conductors are impressed upon a band-pass filter 543, the output of which is connected to the primary winding of transformer 544. The reason for providing bandpass filters 532 and 543 is that the conductors 533 and 534 may carry a plurality of outgoing messages simultaneously, the different messages being characterized by different frequencies of signaling current and the conductors 54| and 542 may carry a plurality of incoming messages similarly differentiated. The band-pass filter 532 suppresses frequencies other than those intended to be transmitted from the oscillatory current source 52E and the filter 543 suppresses from the primary winding of transformer 544 all but one message frequency or band of frequencies.

The secondary winding of transformer 544 is connected to the grid circuit of an amplifier tube 546, the anode circuit of which is coupled through a resistance capacity coupling to a second stage amplifying tube'541. The anode circuit of tube 541 includes, the primary winding of an output transformer 548, the secondary winding of which is center tapped and is connected in a full-wave rectier circuit 550 similar to that previously described comprising the hybrid coil windings 5| 1 and 5|8, the rectiers 522 and 523 and condenser 5|9 shunted by resistor 52|. The rectier circuit 550 controls the flow of current from a source of oscillatory current 549 through the primary winding of a transformer 55| having a half-wave rectifier 552 in the same relation to source of oscillatory current 549, the rectifier circuit 550 and the primary winding of transformer 55| that rectifier 53| has to source of oscillatory current 526, the full-wave rectier circuit which includes condenser 5|9 and the primary winding of transformer 529. Thus marking intervals of oscillatory current received over the line conductors 54| and 542 are amplified in the two-stage amplier and are transposed into marking signals of nocurrent condition in the secondary of transformer 55|. The secondary of transformer 55| is connected to the input of a band-pass lter 553, the

output of which is connected into the hybrid coil 5 6 whereby the transposed signals are impressed on conductors 402 and 406 by which they are conducted to the cord 250.

Transformer' 548 has a tertiary winding which is connected across the input terminals of a full-wave bridge rectier circuit 554, the output circuit of which includes resistor 556, condenser 551 shunted across resistor 556, and a series oi two condensers 558 and 559 shunted across condenser 551, the condenser 558 having a resistor 56| in shunt therewith. From the point of interconnection of condensers 5,58 and 559, conductor 562 is connected back to the grid circuit of ampliiier tube 546. The rectifier circuit 554 and associated apparatus serves as an automatic gain control system, rectifying a portion of the output of the second stage amplifier tube 541 and applying back to the grid circuit of tube 540 over conductor 562 a biasing voltage which supplements the normal biasing voltage provided by the cath- 0de resistor of tube 546 and which varies inversely as the signal level. When a weak signal is impressed upon the grid of tube 546, the voltage impressed across rectifier circuit 554 is less than when a strong signal is received and accordingly tube 546 is biased less negatively as a result of reception of a weak signal than of a strong signal, thus a substantially constant level of signal impressed on the secondary of transformer 548 canbe maintained.

The automatic gain control feature having been described, the reason for the transposition of signals so that the trunk circuits shall carry oscillatory current for the marking condition and no current for the spacing condition may be explained. The idle condition of conductors 533 and 534 will be the marking condition with oscillatory current flowing, since, with no current flowing in conductors 402 and 40S, whether because of the fact that no plug is inserted into jack 40| or because of an idle interval or lull in communication between two stations connected over the trunk circuit, the signal rectier in the transposition circuit will be receiving no signal and accordingly oscillatory current from oscillator 526 will be iiowing in the primary winding of transformer 529. The same condition will be true with respect to line conductors 54! and 542 so that during the idle time the amplifier comprisingtubes 546 and 541 will be amplifying the received marking signal and the gain of the amplifier wil be held down by the rectified portion of the signal in the automatic gain control apparatus. When spacing intervals of no current are received over conductors 54| and 542, the gain of the amplifier will tend to rise but the condensers in the ouput of the rectifier circuit 554 will delay such rise. If no signal transposition had been provided in the trunk circuit, there would be no current during the idle or marking condition and the biasing voltage supplied by the automatic gain control circuit would substantially or completely disappear thus greatly increasing the sensitivity of the amplier so that extraneous disturbances received over the conductors 54| and 542 might disturb supervisory apparatus which is under the control of signals, as is described in the copending application, and abnormal amplification of the first train of oscillatory current received upon the initiation of transmission might result.

The receiving circuit terminating the intertoll trunk conductors S33-534 and 541-542 at the remote central office station is represented diagranimatically in Figs. ll and is designated by reference numeral 50|. It has a terminating jack 5il2 from which a call may be extended by means of a cord circuit 503 to a jack terminating a subscribers li-ne or other communication circuits. v

It may be desirable to extend a call over another intertoll trunk to reach a subscriber station fservedby'still'anothericentralxoice station. The

communication path from 'one subscriber: station to the other would then include at least two intertoll trunks connected in tandem. Because `of the fact that signals transmitted `over long distances, although repeated and amplified in .the intertoll trunk circuit, may deteriorate due ito distortion, which distortion lis amplified vas .part of the signal by'amplier, such as the one shown in Fig. l, it may be necessary to restore the signals totheirorginal condition'by means of a vregenerative repeater-which may be located at vone or more intermediate central office staytionsand throughwhich the intertoll trunks are interconnected. Accordingly the system shown in Fig. 3 represents, from left to right, a subscriber station and'line circuit equipped to transmit alternating-current signals, a central oice cord circuit andoperators set, an intertoll trunk ycircuit equipped to transmit alternating-current signals, a cord circuit, all of the foregoing being shown in Fig. l, a regenerative repeater having terminal jacks, shown in Fig. 2, and a duplication of all of the apparatus and circuits shown in Fig. l, arranged in reverse order, and ultimately terminating in a. subscriber station.

The structure and operation of the regenerative repeater will be described first upon the basis of regeneration of a code signal combination entering the repeater through cord circuit 503, jack 102 and the left-hand winding of transformer 80|. It should be borne in mind that since the signalsenter the repeater through a cord circuit, the transmission into, through and Yout of the cord circuit, and into the regenerative repeateris upon .the ybasis of no current forthe marking condition .and alternating-current trains for the spacing condition, the transposition from the intertoll :trunk transmission condition having occurred in `the intertoll trunk terminating circuit 50|. Ac-

cordingly in the normal or idle marking condition no current is impressed upon the left-hand wind- 'ing of transformer 80 l. The upper right-hand 'hand winding of transformer 80| into the lower right-hand winding will have no effect since the latter winding is in the output circuitof avacuum tube. Accordingly signals impressed on the left- "hand winding of transformer 80| are routed through tube 803 in which spacing impulses of oscillatory current are amplified. The grid circuit of tube 803 includes a resistorfor reducing the gain of the tube when the grid ybecomes positive. Amplified spacing signals are impressed across the left-hand or primary winding of the transformer 808 included in the anode circuit of tube 803. Accordingly, corresponding alternating current is induced in both of the right-hand or secondary windings of the transformer. A bridge type full-wave rectiner 801 is connected across the upper secondary winding of transformer 806 and a condenser 808 shunted by a resistor 009 is connected across the output of rectifier 801. rIkhus direct current resulting from the rectication of a spacing train of alternating current will result in the charging of condenser 808.

The lower secondary winding of transformer 80.5 has two half-wave rectifiers connected to the ends thereof to form a full-wave rectifier circuit Aand the 'output of this rectifier circuit includes variable resistor 8|| and condenser 8|2 in series. Thus the rectified spacing current will charge condenser SI2 through thevariable resistor 8| The variable resistor controls the timing of the charging of condenser 8|2 and thereby serves as an orientation adjustment to .permit the most effective part of a received impulse to control the retransmission of a corresponding impulse inregenerated manner. The grid circuit of a hot cathode gas-filled trigger tube 8|3, the grid of which isnorinally biased sufciently negative by kbattery'8IlI to prevent firing of the tube, is connected across the condenser SI2 and when ka sufcientipositive charge has been developed .across condenser SI2 asa result of the rectification of `a spacing signal, which will be assumed to be the start impulse of a permutation code signal, the -gridfof tube 8|3 wili be renderedsuiciently positive to re the tube. With tube 8|3 rendered conductive, the potential of its cathode is suddenly rendered considerably more positive lwith respect to ground due to current through the cathode resistor. Thecathode of tube 8|3 is connected by conductor SI5 to the cathode of an amplifier tube 8|"I, the grid circuit of which iS connected vacross the upper left-hand or secondary-winding of transformer 802, and which stands inthe same relation to transformer 802 that vacuum-tube 803 bears to transformer 80|,.namely, thatftube 8 I1 serves to amplify spacing trains of alternating current impressed on the righthand or primary winding of transformer 802 through jack '|01 from a remote station and induced by the primary winding of transformer 802 into the upper secondary winding. By virtue oftheinterconnection of the cathodes of tubes 8 |3 and 8 I through conductor 8 5, the cathode vof amplifiertube 8 'i is made considerably more posi-l -tive with respect to ground, thereby increasing the bias on tube 8|? well beyond the cut-off point oi that tube so that it is rendered completely unresponsive to any spacing signal which might be received through jack 101 from a remote station. Any attempted transmission of signals through the yrepeater in the opposite direction from that now being considered is prevented,

The cathode lof gas-filled tube 8|3 is also connectedthroughcondenser 8I8 and conductors 8|9 and 82| to the cathode of a hot cathode gas-filled trigger tube 822 which is at this time conducting, not because its grid is above the firing potential but. because its grid was previously raised momentarily above the firing potential, as will be later described, and it is acharacteristic of such tubes that having been red, they cannot be out off by reducing Athe potential of the grid but can only be quenched by opening the external circuit between the anode and cathode or in some other manner reducing the potential diiference between the anode and the cathode. Due to the raising of the potential of the cathode of gas-filled tube 8 I3 aboveground, an impulse is applied through condenser V818 and conductors 8 9 and 82| which vmomentarily makes the cathode of tube 822 more positivewith respect to ground than it had vpreviously been, thus reducing the potential difference between the cathode and the anode to a value less than sufficient to sustain current between the anode and cathode so that tube 822 1s rendered non-conductive.

The anode circuit of gas-lled tube 822 includes a tapped primary winding of a transformer 823 which is tuned by a condenser 824, and

a portion of which is connected between the 826, with the remainder of the transformer pri mary connected between the cathode and anode of that tube. This will be recognized as an electron tube oscillator circuit and the constants of the primary of the transformer 823 and of condenser 824 are such that the frequency of oscillation is equal t one cycle per impulse interval of a permutation code signal. When gas-filled tu-be 822 is conducting, the flow of its anode current through the primary winding of transformer 823 prevents tube 826 from generating oscillatory current. However, when tube 822 is rendered non-conductive the oscillator circuit comprising tube 826, transformer primary 828 and condenser 821i begins to oscillate, and its circuit constants are such that it begins substan* tially at the zero point of the voltage wave substantially without a transient.

The oscillator voltage is impresed on the grid of tube 828 through the secondary winding of transformer 823 poled so that the grid becomes less positive during the first half ofthe wave. Tube 828 flashes at a part of the wave which is predetermined by the circuit constants. The anode of tube 829 is connected through conductor 83! to one terminal of a condenser 832, the other terminal of which is connected to the anode of a hot cathode gas-nlled trigger tube 836. Upon the firing of tube 828, an impulse is delivered through the condenser 832 which reduces the potential of the anode of tube 885 and if this tube has been conducting, it is quenched. The anode circuit of tube 829 includes the primary winding of a transformer 837 which has a plurality of secondary windings. The primary of transformer 833' is shunted by a condenser 838. The condenser 838 delays the building up of a iiow of anode current through the primary of transformer 881 until after tube 829 has quenched tube 838 if the latter has been conducting. By the time such quenching action has been accomplished, a sharply peaked impulse passes through the primary winding of transformer 83? and induces a similar impulse in the secondary winding 838. One terminal of secondary winding 839 is connected through biasing batteries to the cathode of gas-filled tube 838 and the other terminal of the secondary winding 839 is connected to one terminal of condenser 808 which, together with resistor S88 in shunt therewith, is connected across the output of full-wave rectifier 887. The other terminal of condenser 888 is also connected to the grid of gas-filled tube 836. The polarity of the impulse generated in transformer secondary S38 is in series-aiding relation to the charge impressed on condenser 888 as a result of rectication of the received start impulse which, being of spacing nature, is represented by received alternating current and the potential across the transformer secondary 839, added to the potential across condenser 888 is sufficient to fire gas tube 835. The reason that tube 829, upon firing, was able to quench tube 836 through condenser 832, although a potential was then being developed across condenser 888 due to the rectification of the start signal, is that the voltage which can be developed across condenser 888 by rectier 881 is insulicient to nre tube 835. It may also be added that the voltage developed across transformer primary 839 is insufcient to re tube 888 except when aided by a voltage across condenser 888. Thus the tube 836 can be fired only when a spacing train of alternating current is being received and rectified and can be fired only under the timing control of transformer' 837.

The cathode of tube 836 is connected by conductor 831 to the grid of an amplifier tube 838. Tube 833 has a source of alternating current -846 generating oscillatory current at the signaling frequency connected from cathode to ground. When tube 838 is non-conductive, a steady negative bias is applied to the grid of vacuum tube 838 so that the tube is biased well below the cut-ofi point and even the positive swing of the alternating current from source 846 will not raise the potential or the grid of tube 838 sufiiciently to render the tube conducting. However, when tube 838 becomes conductive the potential of the grid of tube-88B is raised sufiiciently that tube 838 is rendered conductive, the conductivity being varied in accordance with the control of the cathode potential by the source of oscillatory current 886 and the tube will thus serve as an arnplier of the oscillatory current at the signaling frequency. The anode circuit. of tube 838 ncludes the lower left-hand winding of transformer 882 so that there will be induced in the righthand winding and transmitted to the cord circuit connected to jack l'i a train oi' oscillatory spacing current representing the start signal. The duration of this start signal will not be dependent upon reception of a start signal of effective amplitude during the entire start signal interval, since the gas-iilled tube 838, having been rendered conductive in consequence of the charging of condenser 888 due to reception of a start signal, at least a portion of which is of effective amplitude, cannot be quenched by grid control even though the received start signal may trail oli to insignicant amplitude before the end of the start signal interval, due to distortion. Tube 838 can be cut off only by tube 828 under the control of oscillator tube 828 in a manner heretofore described, whereby there will be allotted to the transmission of the start signal by tube 838, a full start signal interval, which will be recognized as constituting regeneration of the signal.

It will be observed that the cathode return circuit of tube 829 includes a resistor 848 shunted by a condenser 849. Upon the ring of gas-filled tube 829 under the control of oscillator tube 826, the inductance of the primary winding of transformer 831 through which the anode current of tube 829 ows causes condenser 8:39 to become charged to such potential that the potential difference between the anode and cathode of tube 829 is reduced below the value at which a discharge may be maintained, and tube 828 is quenched. Following the quenching of the tube condenser 849 discharges through resistor 888 which retards the discharge so that tube 829 has time in which to deionize before condenser 849 has completely or almost completely discharged and has thus restored the normal potential difference between the anode and cathode of tube 829. The actual time of ring of tube B29 is just after the oscillator voltage has begun to rise above zero in the positive half cycle. Tube 829, upon being quenched by condenser 849, remains nonconductive under the control of the condenser, due toits slow discharge, until after the oscillator has entered its negative half cycle. Accordingly,

tube 829 does not refre in the same positive half cycle, but awaits rering in the next positive half cycle. As previously stated, the oscillator is` adjusted to produce one cycle per impulse interval of a permutation code combination. Thus for each cycle ofthe oscillator, tube 829 is rendered conductive and remains so only momentarily" 11 due to the self-quenching effect of condenser 848so that a succession of impulses is produced with a time interval between each two impulses equal to the signaling impulse interval of permutation code signals.

Transformer 831 has other secondary windings designated by the reference numerals 85|, 852, 853, 854 and 856. Secondary Winding 852 of transformer 831 is connected in the grid circuit of a hot cathode gas-filled trigger tube 851,.so that tube 851 is fired at the same time thattube 836 is red in response to the first impulse in the primary Winding of transformer 831. The cathode of gas-filled tube 851 is connected through the secondary Winding 853 of transformer 831 to the control anode of the first of six cold cathode gas-filled electron discharge tubes, the rst tube being designated by the reference numeral `858. The cathodeofthe first cold cathode tube is connected through theV secondary Winding 854 of transformer 831 to the control anode of the second cold cathode gas-filled tube 859. The cathode of the second cold-.cathode tube 858 is connected to the control anode of the third cold cathode tube 86| through secondary winding 856 of transformer 831. The cathode of tube 858 is connected to ground through resistor 862 shunted by condenser 863. The cathode of tube 859 is connected to ground through .resistor 864, shunted by condenser 866. Other cold cathode tubes indicated by the dotted line between tube 86| and the final tube 861 have their cathodes connected to ground through individual resistors shunted by condensers, and the nnal tube. 861 has its cathode connected to ground through resistor 868 shunted by condenser 869. The number of cold cathode tubes employed is de termined by the number of signal elements in the permutation code, each tube serving to count one element of the code. Each of the cold cathode tubes except the final tube 861 has its main anode connected to a conductor v81| through. a resistor and the final tube has its main anode connecteddirectly to the conductor 81|. Conductor 81| is connected through inductance 812.*to the positive. terminal of battery 81 3, the negative ter-"- minal of which is grounded. From thisit Willbe apparent that theinductance. 812; is. common to the main anode circuits of all ofthe-cold cathode.r

gas-filled tubes.

minal of which is connected to the anode of hot cathode gas-filled tube 8|3. A condenser 811 isv connected between the anode of hotcathodegasf.

filled tube 851 and conductor 81| so. thatwhen. tube 851 is fired substantially, simultaneouslyy with tube 836 in responseto the .start signal, an impulse will be delivered through condenser811, conductors 81| and 814 and condenser A816 .tend-1 ing to quench tube 8|3 which is now conductive, it will be remembered, since thestart signal now being received and rectified will have vraisedrthe potential of the grid'of gas-filled tube 8|3. Such impulse will not be effective to quench. tube '813. because it will not be vof sufficient amplitude; Tube 8|3 Will remain active until a. stronger impulseis impressed upon. its. plate, which occurs. when tube v861 flashes, as VWillbe :described here-A inafter.

With tube 851 rendered conductive, the control anode of the first cold cathodeI tubev 858; bee ing` connected to the cathode of tube 851', will be made more positive with respect tol ground'v dueto current in the cathode resistor of tube 85,1.' Tube.'

858 will not fire at this time because condenser voltage peak in transformer secondary 853 subsides. Upon the next energization of transformer 831, under the control of oscillator 826, the-voltage induced in the secondary Winding 853 Will'be added to that already applied to the control anode of tube 858 from the cathode of tube 851 and the aggregate Will be sufficient to fire the control gap of tube 858 which will break down the main gap and cause current to flow in the main anode circuit. Due to the presence of the resistor connected between the main anode of tube 858 and conductor 81|, the potential of conductor 81| will not be materially reduced as the space discharge potential in tube 858 drops from the ring to the sustaining potential so that no impulse will be impressed on condensers 816 or 811 quenches gas-filled tube 836 through conductor- 83| and condenser 832. Since the Signaling impulse is of marking nature, no alternating current will be impressed upon rectifier 801 and accordingly no voltage Will be built up across condenser 838 from the rectifier. Simultaneously with the firing of tube 858, through transformer secondary Winding 853, a pulse will be induced in the secondary Winding 839 of the transformer which Willbe impressed on the grid circuit of tube 836. The voltage of this pulse is of insu'cient magnitude to re tube 836 in the absence of a voltage across condenser 808 and accordingly tube 836 Will not be fired. With the quenching of tube 836 its cathode became more negative, thus biasing the grid of Vacuum tube 838 through conductor 831 to the cut-off point so that oscillatory current from source 846 is withheld from transformer 802 and a 'no-current condition representing a marking impulse is produced in the right-hand Winding of transformer 802. Had the received first code impulse been of spacing nature, the

same as the start impulse, tube 836 Would havebeen quenched momentarily by tube 823 but grid control resulting from the Voltage inducedin secondary Winding 833 of transformer 831 added to tween the two spacing signals.

Gas-filled tube 836 and vacuum tube838 remain in the conditionestablished under the'control ofthe rst code impulse of the code combination until tube 828 is again fired under `the control ofthe oscillator 826 at which time the second codel impulse of the signal `combination isl beingvre-v ceived and the second cold cathode gas-filled tube 859, having had its control anode made more posiv tive with respect to ground due to current through the cathode resistor 862 of tube-858,is fired bythevoltage induced in transformer secondary winding 854. Tubes 83S and 838 are conditioned in accordance with the code impulse then being received and the tube 859 registers the fact that this is the second code impulse of the code combination, there being three remaining code `impulses to be received followed by the stop impulse which is of marking nature. The reception and retransmission of the remaining code impulses are registered or tallied by the third cold cathode tube 86| and by the other cold cathode tubes indicated but not shown.

Upon the actuation of tube 829 following retransmission of the last selecting code impulse, the final cold cathode gas-filled tube 881 is red and tube 836 is quenched without fail if it has been conductive for the final code impulse of the code combination, since the stop impulse is of marking nature and there is no voltage across condenser 86S to aid the voltage induced in transformer secondary 888. Accordingly, tube 838 is unfailingly biased to cut-oit. The anode circuit of cold cathode tube S61 differs from the anode circuits of the other cold cathode tubes in that no resistor is included between the main anode and the conductor 81|. At the instant that the main gap of tube 861 becomes conductive, there is no current in the cathode resistor 868 of tube 881 so that no voltage exists across condenser 868. Accordingly, the full voltage between conductor 81| and ground exists between the main anode and cathode of tube 861. However, it is a characteristic of cold cathode gas-filled tubes that immediately upon firing, the main gap potential decreases to the discharge sustaining potential. Since condenser 869 has not yet had time to absorb the difference between the discharge sustaining potential and the potential which existed between conductor 31| and ground just before tube 861 fired and there is no resistor between the anode of tube 881 and conductor 81| which can absorb this decrease in potential, it must follow that the potential of conductor 81| with respect to ground is decreased, and such decrease, applied through conductor 814 and condenser 816 to the anode of gas-filled tube BES quenches that tube and also quenches tube 851 through condenser 811. Also due to the reduction in the potential of conductor 81|, the potential of the main anode of each of the other cold cathode tubes with respect to its cathode is reduced below the discharge sustaining potential so that those tubes are also quenched. The sudden cutting oii of current through all but the nal one of the cold cathode tubes which have the inductance 812 common to their anode circuit results in a decrease of current through inductance 812 which accordingly develops a counter-electromotive force tending to sustain such current and therefore in series-aiding relation to battery 813. Since the only conductive path for the dissipation of this counter-electromotive force is through the main anode discharge path of tube 861, the anode current in this tube rises to a value above that which would be produced by battery 813 alone and the iiow of this current through cathode resistor 868 raises the voltage across condenser 889 to a higher value than would appear across the condenser if the inductance 812 were not present. When the counter-electromotive force in inductance 812 has Ibeen dissipated, the voltage between conductor 81| and ground returns to the voltage of battery 813. However, since the condenser 869 carries a larger voltage atthis time than it through the cathode resistor. This more positive Y potential than ground applied over conductor 88| and through condenser 882 raises the potential of the grid of tube 822 above the firing potential so that tube 822 is rendered conductive as a result of the tallying of the stop impulse and the anode current of tube 822 flowing through the primary of transformer 823, which is the inductive portion of the character timing oscillator, stops the generation of oscillatory current for timing the impulses of a code combination. The oscillator is critically damped and stops substantially without a transient. Thus the regenerative repeater is restored to the initial condition with none of the tubes therein conductive` except the tube 822, and the circuit awaits lthe reception of the next code combination.

When signals are received in the right-hand winding of transformer 882 through jack 131 to repeated in regenerative manner and retransmitted through jack 182 such signals are received by transformer and are amplified by tube SI1. The anode circuit of tube 8|1 includes the primary winding of a transformer 886 which corresponds to the transformer 886 and which is provided with two secondary windings. The upper secondary winding works into a full-wave rectiiier 881, the output of which controls the hot cathode gas-iilled trigger tube 888 jointly with impulses supplied from transformer 831 through the secondary winding Tube 888 corresponds to tube 838. The lower secondary winding of transformer 888 has rectiiiers associated therewith for charging condenser 889 to control hot cathode gas-lled trigger tube 89| which corresponds to tube 8|3 and which is effective in response to the start impulse of a code combination for disabling tube 883 which arnpliiiessignals received over conductors 833 and 834 so that there can be no interference with the transmission of a complete code combination.

The impulse timing and counting circuit coniprising start tube 822, oscillator 828, oscillator impulse detector tube 829, and counting chain tubes 851, 358, 859, 85| and 861 are common to both of the retransmitting tubes 836 and 888 and to both interference preventing tubes 8 3 and 88 i the intercircuit controls previously described be-I ing effective over the common conductors 8i9, 83| and 814.

Although certain specinc embodiments of the invention have been shown in the drawings and described in the foregoing specification, it will be understood that the invention is not limited to such specific embodiments but is capable of modication, rearrangement and substitution of parts and elements without departing from the spirit of the invention and within the scope of l the appended claims.

What is claimed is:

1. In a signaling system for transmitting oscillatory signaling current, a signal transferring device adapted to transfer only oscillatory cur#- rent, arectiiier device for deriving a unidirectional potential froml oscillatory current trans- 'erred bysaid transferring device, a source of oscillatorysignaling current, and keying meansv controlled'n accordance with the operation' of said rectifier device for controlling transmission from said source.

2. In arepeater'for signals comprising trains of oscillatory current, means for rectifying received trains of oscillatory current, a source of oscillatory signaling current, and keying means controlled in accordance with the operation of said rectifying means for controlling oscillatory current rsignalretransmission from said-source.

3. Ina signaling channel for transmitting oscillatory signaling currents, a signal transposing device-comprising a full-Wave rectifier for rectifying signaling current flowing into said channel, means for generating oscillatory `signaling currents to be transmitted onvvardly through said channel, and means controlled by said rectifier when rectifying signaling current flowing into said channel for estcpping the now of signaling current onvvardly throughsaid channel from said source.

4. In a'signaling channel for transmitting oscillatory signaling currents, a signal transposing device comprising a full-Wave rectifier for rectifying signaiing'current flowing into said channel, means for generating oscillatory signaling current to be transmitted onwardly through said channel, and a condenser in the output of said rectierchargeable thereby to'estop the flow of oscillatory current onwardly through said channel from said source during rectification of signaling current flowing into said channel.

5. In a signaling channel for transmitting oscillatory signaling current, a signal transposing device comprising afull-Wave rectmer for rectifying oscillatory signaling current received over said channel from the remote-end thereof, means for generating oscillatory current to be transmitted onwardly through said channel, a condenser in the Voutput of said rectier chargeable thereby tofestcp-the now of oscillatory current onwardly through said channel from said source during rectincation of signaling current received over said channel from the remote end, a supervisory relay controlled'according to the potential developed across said condenser' by said'rectier, and means controlled` byl said relay for registering supervisory operation ofV said relay.

6. In a regenerative repeater for telegraph signals comprising trains of alternating current, meansfor rec'tifying received' trains of oscillatory currentJ aA normally deactivated source of timing impulses Vhaving ar frequency corresponding to the desired telegraph code impulse frequency, means controlled by said rectifying means'for activatingsaidsource of timing impulses, means for counting the timing impulses produced by said source, a source of oscillatory signaling current, meansfor keying said source of oscillatory signaling current, and means' controlled jointly by said' re'ctifying means and'said' source of timing impulses for controlling saidl keying means.

7.*In a `regenerative repeater for telegraph signals' comprising' trains of oscillatory current, means for rectifying said trains of oscillatory currentV a normally deactivated source of timing impulses having a frequency corresponding to' the desired telegraph code impulse frequency, means for activating and' deactivating' said lsource of timing impulses, means controlled by said'rectifying means for causing said activating` and cleactivat'ing` means to activate said source of timingimpulses, meansior counting the'tim'- ing-v impulses produced by said source, a source of' oscillatory signaling currenty means for keying said source o' oscillatory signaling current, means controlled jointly by said rectiiying means and saidv source of timing impulses'iorcontrolling said keying meansgand means controlled by said' counting means uponcounting -a predetermined nur'nber'l of saidv timing impulses for causing-said'.

activating and deactivating means to deactivate said source-of timing impulses.

`8. In `a regenerative repeater for telegraph signals comprising trains of oscillatory current,`

timing current, means for counting said impulses,

a source of oscillatory signaling current, means for keying said source of oscillatory signaling current, means controlled jointly by said'rectifying means andisaid impulse deriving means for controllingsaid keying. means, and measl controlled bysaid counting meansV upon counting. a predetermined'number of impulses for causing said activating and deactivating means to deactivate said source of oscillatory timing circuit.

9. In a regenerative repeater for telegraph signals comprising trains of oscillatory current, two rectiflers for simultaneously and independentlyfrectifying received trains of oscillatory current, afnormally deactivated source of timing impulses having a frequency corresponding to the' desired telegraph code impulse frequency, means for activating and deactivating said source ofV timing-impulses, means controlled by one of .said rectifiers for causing said activating and deactivating--means-to activatefsaid source of timing impulses, y*means for countingthe timing impulses produced by said source, a source of oscillatory signaling current, means for keying. said source of oscillatory signaling current, means controlled jointly by the other of said rectiers and said source oftiming impulses for controlling said keying means, and means controlled by said counting .means upon lcounting a predetermined number of impulses for causing said activating and deactivating means'to deactivate saidsource of timing impulses.

10. In' a regenerative repeater for telegraph signals comprising trains of oscillatory current', means for rectifying received trains of oscillatory current, a Anormally deactivated source of oscillatory'timing current having a frequency'correspending to the desired telegraph code impulse frequency, means' for activating and deactivating said timing current source, means controlled by said rectifying means for causing said activatingl and deactivating means Vto' activate said timing current source, an electron discharge tube acti# vated once for each cycle of timing current'fr'om' said source, means for counting the successive activations of saidv tube, a source of oscillatory signaling current, means for keying said source of oscillatory signaling current, an electron discharge tubew deactivated by saidrst-mentioned electron discharge tube if conductive at the time of activation of said first-mentioned electron discharge tube and subject to immediate reactivation under the joint control of said first-mentioned electron discharge tube and said rectifying means for controlling said keying means, and means controlled by said counting means upon counting a ypredetermined number of activations of said first-mentioned electron discharge tube for causing said activating and deactivating means to deactivate said timing current source.

11. In a regenerative repeater for telegraph signals comprising trains of oscillatory current, means for rectifying received trains of oscillatory current, a normally deactivated source of oscillatory timing current having a frequency corresponding to the desired telegraph code impulse frequency, means for activating and deactivating said timing current source, means controlled by said rectifying means for causing said activating and deactivating means to activate said timing current source, an electron discharge tube activated once for each cycle of timing current from said source, means for counting the successive activations of said tube, a source of oscillatory signaling current, means for keying said source of oscillatory signaling current, an electron discharge tube deactivated by said first-mentioned electron discharge tube if conductive at the time of activation of said first-mentioned electron discharge tube and subject to immediate reactivation under the joint control of said first-mentioned electron discharge tube and said rectifying means for controlling said keying means, means associated with said keying means for momentarily delaying response of said keying means to deactivation of said second-mentioned electron discharge tube whereby to aord continuity of signal transmission attending immediate reactivation of said second electron discharge tube, and means controlled by said counting means upon counting a predetermined number of activations of said inst-mentioned electron discharge tube for causing said activating and deactivating means to deactivate said source of timing current.

12. In a regenerative repeater for telegraph signals comprising trains of oscillatory current, a pair of transformers each terminating a telegraph line, means associated with each transformer for rectifying oscillatory current received over its associated line, means associated With each transformer for impressing oscillatory signaling current on its associated line, a normally deactivated source of oscillatory timing current having a frequency corresponding to the desired telegraph code impulse frequency, means for activating and deactivating said timing current source, means controlled by each of said rectifying means upon response thereof to signals impressed on its transformer by its associated line for Withholding signals from the rectifying means associated with the other transformer and for causing said activating and deactivating means to activate said timing current source, means for counting the timing impulses produced by said source, means controlled jointly by said source of timing impulses and the rectifying means associated with either of said transformers for activating the signal impressing means associated with the other of said transformers, and means controlled by said counting means upon counting a predetermined number of timing impulses for causing said activating and deactivating means to deactivate said source of timing impulses.

LELAND C. ROBERTS.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 1,521,671 Deardorif Jan. 6, 1925 1,521,685 'Hamilton Jan. 6, 1925 2,404,754 Simpson July 23, 1946 2,417,543 Chapin Mar. 18, 1947 2,495,805 Bliss Jan. 31, 1950 

